Since the beginning of oil production from subsurface formations, the industry has been concerned with efficient control of the movement of unconsolidated formations particles, such as sand, into the well bore. For example, such formation movement commonly occurs during production from completions in loose sandstone or following hydraulic fracture of a formation. Production of these materials causes numerous problems in the operation of oil, gas or water wells. These problems include plugged formations, tubing and subsurface flow lines, as well as erosion of casing, downhole equipment and surface equipment. These problems lead to high maintenance costs and unacceptable well downtime. Accordingly, numerous methods have been utilized to control the movement of these unconsolidated formations during the production of fluids.
Gravel packing is one of the most common methods to prevent the production of sand. Generally, gravel packing involves placing pack sand, an aggregate or particulate material, in the annular space between the well bore and a fluid permeable, perforated base pipe that is located adjacent to the production zone. The pack sand is selected to prevent the flow of formation particles therethrough, taking into consideration the characteristics of the particular reservoir. The perforated base pipe is designed to allow production fluids to flow therethrough with minimum resistance, while preventing both the pack sand and the formation particles from flowing into the production string. Gravel packing is commonly achieved by either an open hole gravel packing procedure or an internal gravel packing procedure, depending on the characteristics of the particular reservoir.
In addition to the use of a perforated base pipe and gravel packing, a sand-control screen is commonly employed to control the movement of formation particles. These screens may comprise a continuous single wire mesh wrapped around the base pipe. While this type of screen is capable of excluding even the smallest API grades of pack sand, these screens are easily damaged during handling, installation and production.
More recently, a sand-control screen comprising a screen jacket has been used. The screen jacket is fully formed from a single wire prior to attachment to the base pipe. Commonly, a plurality of rods extend longitudinally along the internal surface of the screen jacket to provide strength to the wire and stand-off between the wire and the base pipe once the screen jacket is attached. Even with the use of screen jackets in conjunction with gravel packing, however, it has been found that formation particles may migrate through the pack sand, eroding channels therethrough. Once these channels are formed, additional formation particles travel therethrough with minimum resistance, thereby continuing the erosion process within the pack sand and allowing formation particles to travel through the screen jacket and enter the interior of the base pipe.
To reduce the possibility of channeling, some screen designs use prepacked sand confined around the perforated base pipe. These prepacked screens are constructed by fabricating the metal components, then forcing pack sand, either resin-coated or uncoated, between the perforated pipe and an inner wire screen or between an inner wire screen and an outer wire screen of a multi-layer screen.
Typically, whether single or multi-layer, conventional or prepacked, the screen jacket is secured to the base pipe by welding. The process for welding a screen jacket to a base pipe, however, is sometimes very difficult due to the difference in metallurgy of the components. For example, the material used for the base pipe may be 13 chrome while the material used for the screen jacket may be a special alloy such as 304 stainless steel, 316 stainless steel, Hastelloy, Inconel, or Monel. Due to the difficulty of the welding process and the post-weld heat treatment, which is required due to the differences in metallurgy of the screen jacket and the base pipe, there have been numerous failures in the connection between screen jackets and base pipes. For example, cracking within the welds as well as in the heat affected zone has been noted.
In addition, both the welding process and the post-weld heat treatment have resulted in a poor sealing between the screen jacket and the base pipe. The use of typical elastomeric seals has proven to be inadequate due to their inability to withstand the high temperatures required during these processes. This lack of an adequate seal may result in longitudinal flow of production fluids and more critically, formation particles between the screen jacket and the base pipe.
Therefore, a need has arisen for an apparatus and a method for attaching a sand-control screen jacket to a base pipe that does not require welding and that allows for a seal between the screen jacket and the base pipe. A need has also arisen for an apparatus that is simple and cost-effective to manufacture and assemble and which is capable of withstanding severe downhole conditions during installation and production.